klibc - Aug 2010 - Bug#594638: klibc-utils: ipconfig assumes dhcp server is nameserver

On Fri, 27 Aug 2010, Vagrant Cascadian wrote:
> 
> ipconfig apparently assumes that the dhcp server's ip address is the
> nameserver when dhcp gives it no nameservers, dhcp gives the nameserver
> 0.0.0.0, or the nameservers are not ip addresses (i.e. ns1.example.org).
> while these scenarios are probably not extremely common, i'm not sure
> this is a good default with no way to disable it. 
hmm, several questions at mind, what do you mean my "dhcp gives the
nameserver" is this the ISC dhcp 3 client?

is that really a sensible thing to do?
what do standards say (aka RFC's pointers)?

we could set it to the public available google server,
as this one might be better working as this guess of
the el cheapy router box?

 
> it prints out the message:
> 
>   IP-Config: eth0 guessed nameserver address 192.168.0.1
according to git history this was added on day 0 of ipconfig,
not that this would justify it.
 
thanks for your input.

-- 
maks

On Tue, Aug 31, 2010 at 02:21:56PM +0200, maximilian attems
wrote:
> On Fri, 27 Aug 2010, Vagrant Cascadian wrote:
> > ipconfig apparently assumes that the dhcp server's ip address is
the
> > nameserver when dhcp gives it no nameservers, dhcp gives the
nameserver
> > 0.0.0.0, or the nameservers are not ip addresses (i.e.
ns1.example.org).
> > while these scenarios are probably not extremely common, i'm not
sure
> > this is a good default with no way to disable it. 
> 
> hmm, several questions at mind, what do you mean my "dhcp gives the
> nameserver" is this the ISC dhcp 3 client?
in this case, i tested with isc-dhcp-server, with the domain-name-servers
option:

  option domain-name-servers ns1.example.org, ns2.example.org;

or
  
  option domain-name-servers 0.0.0.0;

or having no domain-name-servers specified.

though i suspect any DHCP server configured with one of the above mentioned
cases would trigger the issue in ipconfig.

i know the udhcpc client doesn't respond in the same way, haven't yet
tested
isc-dhcp-client.
> is that really a sensible thing to do?
> what do standards say (aka RFC's pointers)?
i don't know off the top of my head... i'll look into it a bit more.
 
> we could set it to the public available google server,
> as this one might be better working as this guess of
> the el cheapy router box?
without reading RFC's, it doesn't necessarily seem invalid to me to have
no
nameservers on a network, and supplying a guessed default may cause problems.
  
> > it prints out the message:
> > 
> >   IP-Config: eth0 guessed nameserver address 192.168.0.1
> 
> according to git history this was added on day 0 of ipconfig,
> not that this would justify it.
i didn't notice the issue till recently, when we configured ltsp to actually
use the nameserver configuration that ipconfig recieves from the DHCP reply
(Debian Bug #593770), and decided to play around with some unusual
corner-cases...

thanks for working on ipconfig!

live well,
  vagrant